The present invention relates to a gas discharge light-emitting device, such as a plasma display device, a noble-gas barrier discharge lamp, and an electrodeless discharge lamp, which is used for image display in computer monitors, televisions, and the like, and a manufacturing method for the gas discharge light-emitting device.
FIG. 10 is a sectional view showing a construction of a panel part of a conventional AC (alternating current) plasma display device.
In the drawing, reference numeral 201 denotes a front glass substrate. A plurality of pairs of display electrode lines 202 are formed in parallel with each other on the front glass substrate 201. A dielectric glass layer 203 is formed over the display electrode lines 202. A protective layer 204 made of magnesium oxide is formed on the dielectric glass layer 203.
Reference numeral 211 denotes a back glass substrate. Address electrode lines 212 are formed on the back glass substrate 211. A visible light reflective layer 213 is formed over the address electrode lines 212. Barrier ribs 214 are formed in parallel with each other on the visible light reflective layer 213, so as to alternate with the address electrode lines 212. Phosphor layers 215 of the three colors (red phosphor layers 215R, green phosphor layers 215G, and blue phosphor layers 215B) are provided in turn to the gaps between adjacent barrier ribs 214. When excited by vacuum ultraviolet light of short wavelength (147 nm) which is generated as a result of discharge, the phosphor layers 215 emit light.
Example phosphors of the three colors typically used are given below:
Blue phosphor: BaMgAl10O17:EU
Green phosphor: Zn2SiO4:Mn or BaMgAl10O17:Mn
Red phosphor: YBO3:Eu or (YxGd1xe2x88x92x)BO3:Eu
Here, a part that is made up of the front glass substrate 201, the display electrode lines 202, the dielectric glass layer 203, and the protective layer 204 is called a front panel, whereas a part that is made up of the back glass substrate 211, the address electrode lines 212, the visible light reflective layer 213, the barrier ribs 214, and the phosphor layers 215 is called a back panel.
Discharge spaces 220 are formed between the front panel and the back panel. A discharge gas that is a noble gas mixture of a predetermined composition (e.g. a gas mixture of helium (He) and xenon (Xe) or of neon (Ne) and xenon (Xe)) is enclosed in the discharge spaces 220 at a predetermined pressure (about 13.3 kPa (100 Torr) to 80 kPa (600 Torr)).
The illumination principle of this plasma display device is fundamentally the same as that of a fluorescent lamp. Voltages are applied to the electrodes to initiate glow discharge, which causes the discharge gas to generate ultraviolet light This ultraviolet light excites the phosphors to emit light.
A specific example of a manufacturing operation of the plasma display device is given below.
The address electrode lines made of silver are formed on the back glass substrate The visible light reflective layer made of dielectric glass is formed on the back glass substrate on which the address electrode lines have been arranged. The barrier ribs made of glass are formed on the visible light reflective layer at a predetermined pitch.
Phosphor pastes of the three colors that each include a different one of the red, green, and blue phosphors are applied in turn to the channels formed between adjacent barrier ribs. The result is fired at a predetermined temperature (e.g. 500xc2x0 C.), to form the phosphor layers of the three colors.
Once the phosphor layers have been formed, a low-melting point glass paste is applied to the periphery of the back glass substrate as a sealing material that seals the back glass substrate and the front glass substrate together. The back glass substrate is then subjected to pre-baking at a predetermined temperature (e.g. 350xc2x0 C.), to remove a resin component and the like from the low-melting point glass paste.
Meanwhile, the display electrode lines, the dielectric glass layer, and the protective layer are formed in this order on the front glass substrate, to form the front panel.
The front panel and the back panel are placed one on top of the other so that the display electrode lines cross over the address electrode lines at right angles and the dielectric glass layer face the barrier ribs. The two panels are heated at a predetermined temperature (e.g. 450xc2x0 C.) to seal them together (sealing process)
After this, the inside of the panel is evacuated to produce a vacuum while heating at a predetermined temperature (e.g. 350xc2x0 C.) (evacuation process). The discharge gas is then enclosed at a predetermined pressure (discharge gas filling process).
In the gas discharge light-emitting device manufactured in this way, lower discharge voltages are desirable in order to reduce power consumption. To attain lower discharge voltages, special techniques need to be incorporated in the manufacturing operation.
It is also desirable to improve luminous characteristics. To do so, the phosphor characteristics need to be kept from degrading throughout the whole manufacturing operation. It is generally known that a phosphor suffers thermal degradation during the sealing process. To suppress such thermal degradation, special techniques need be incorporated in the manufacturing operation.
In view of the above problems, the first object of the present invention is to provide a gas discharge light-emitting device such as a plasma display device that achieves low discharge voltages, and a manufacturing method for the gas discharge light-emitting device.
The second object of the present invention is to provide a gas discharge light-emitting device in which phosphors are protected from thermal degradation during the sealing process of the manufacturing operation and which achieves low discharge voltages, and a manufacturing method for the gas discharge light-emitting device.
The first object can be fulfilled by a gas discharge light-emitting device in which a discharge space filled with a gas medium is formed and which uses a discharge of the gas medium in the discharge space, characterized in that the gas medium includes 0.01% to 1% by volume of water vapor.
With this construction, the water vapor in the gas medium delivers a function of amplifying electrons at the time of discharge. This makes it possible to reduce a voltage which is applied to display electrodes to cause discharge (discharge voltage). Which is to say, when colliding with electrons, the water vapor discharges electrons more easily than a discharge gas such as a noble gas. This electron discharge reaction tends to proceed in a cascade-like manner. As a result, electrons are amplified remarkably.
It was found through experimentation that an optimum value for the water vapor content is in a range of 0.01 to 1% by volume to maximize this water vapor function. If the water vapor content is below 0.01% by volume, the electron amplification function of the water vapor will not be so remarkable. It may appear that the effect of reducing the discharge voltage is more remarkable if the water vapor content is greater. However, if the water vapor content exceeds 1% by volume, the discharge voltage begins to rise. Also, if the water vapor content exceeds 1% by volume when the device is used at a low ambient temperature (below freezing), the water vapor condenses into droplets on the walls that enclose the inner space. This produces undesirable effects.
Here, the gas medium may include at least one noble gas selected from the group consisting of helium, neon, xenon, and argon.
Here, electrodes and phosphors may be provided at least in a periphery of the discharge space, wherein the phosphors (a) are excited by one of ultraviolet light and vacuum ultraviolet light which is generated as a result of the discharge in the discharge space, and (b) emit visible light.
Here, surfaces of the electrodes may be covered with a dielectric.
With this construction, it is possible to prevent electrode degradation which is caused by the water vapor being adsorbed on exposed electrodes. If voltages are applied to electrodes on which water vapor has been adsorbed, the components of the electrodes react with the water and as a result the electrodes degrade. This causes problems such as an increase in resistance.
Here, phosphors may be provided at least in a periphery of the discharge space, wherein one of an electric field and a magnetic field is applied from outside of the discharge space to cause an electrodeless discharge of the gas medium, and the phosphors are excited by one of ultraviolet light and vacuum ultraviolet light which is generated as a result of the electrodeless discharge, and emit visible light.
Thus, the present invention is applicable to various gas discharge light-emitting devices. When the invention is applied to an electrodeless lamp, for example, the water vapor existing in the gas medium delivers the aforementioned function to reduce the discharge voltage.
Here, the gas discharge light-emitting device may be sealed in a state where the phosphors are in contact with a dry gas.
With this construction, the second object can be fulfilled, as the thermal degradation of the phosphors in the sealing process can be avoided.
The first object can also be fulfilled by a manufacturing method for a gas discharge light-emitting device, including: a sealing step for sealing a first substrate and a second substrate which are placed one on top of the other with an inner space in between so that phosphors provided on the second substrate face the inner space; an evacuation step for evacuating the inner space to produce a vacuum, after the sealing step; and a discharge gas filling step for introducing a discharge gas that has an adjusted water vapor content, into the inner space after the evacuation step.
With this construction, the water vapor in the discharge gas exhibits the above function of amplifying electrons at the time of discharge, with it being possible to reduce a voltage applied to display electrodes to cause discharge (discharge voltage). Which is to say, when colliding with electrons, the water vapor discharges electrons easily. This electron discharge reaction tends to proceed in a cascade-like manner. As a result, electrons are amplified remarkably.
Here, the water vapor content of the discharge gas to be introduced into the inner space may be adjusted so that the discharge gas having been enclosed in the inner space has a water vapor content in a range of 0.01% to 1% by volume.
Here, the sealing in the sealing step may be performed with the phosphors being in contact with a dry gas.
With this construction, the second object can be fulfilled.
The first object can also be fulfilled by a manufacturing method for a gas discharge light-emitting device, including: a sealing step for sealing a first substrate and a second substrate which are placed one on top of the other with an inner space in between so that phosphors provided on the second substrate face the inner space; a water vapor introducing step for introducing a predetermined amount of water vapor into the inner space, after the sealing step; and an evacuation step for evacuating the inner space to produce a vacuum, after the water vapor introducing step.
With this method, a desired amount of water vapor remains in the inner space of the completed gas discharge light-emitting device, which enables the above electron amplification function of the water vapor to be delivered. Hence a voltage applied to display electrodes to cause discharge (discharge voltage) is reduced. Which is to say, when colliding with electrons, the water vapor discharges electrons easily. This electron discharge reaction tends to proceed in a cascade-like manner. As a result, electrons are amplified remarkably.
It should be noted that xe2x80x9cthe desired amount of water vaporxe2x80x9d is such an amount that makes the electron amplification action remarkable.
Here, the predetermined amount may be adjusted so that a water vapor partial pressure in the inner space once the water vapor has been introduced is no lower than 1.3 kPa (10 Torr) at a normal temperature.
By adjusting the water vapor partial pressure at no lower than 1.3 kPa (10 Torr), the water vapor remains in the device efficiently. This intensifies the electron amplification action of the water vapor.
Here, a gas medium that includes the water vapor may be introduced into the inner space in the water vapor introducing step.
Here, the introduction of the water vapor in the water vapor introducing step may be performed while construction elements of the gas discharge light-emitting device are being heated in a range of 100xc2x0 C. to 350xc2x0 C.
With this construction, the water vapor remains in the inner space of the completed gas discharge light-emitting device efficiently, which contributes to improvements in discharge voltage reduction effects. Moreover, in this temperature range, the thermal degradation of the phosphors under the presence of water vapor hardly occurs.
Here, the sealing in the sealing step may be performed with the phosphors being in contact with a dry gas.
With this construction, the second object can be fulfilled.
The first object can also be fulfilled by a manufacturing method for a gas discharge light-emitting device, including: a sealing step for sealing a first substrate and a second substrate which are placed one on top of the other with an inner space in between so that phosphors provided on the second substrate face the inner space; and an evacuation step for evacuating the inner space to produce a vacuum, after the sealing step, wherein the sealing step includes a water vapor introducing step for introducing a predetermined amount of water vapor into the inner space, when a temperature is dropping after construction elements of the gas discharge light-emitting device have been heated to a peak temperature.
With this method, a desired amount of water vapor remains in the inner space of the completed gas discharge light-emitting device, which enables the above electron amplification function of the water vapor to be delivered Hence a voltage applied to display electrodes to cause discharge (discharge voltage) is reduced. Which is to say, when colliding with electrons, the water vapor discharges electrons easily. This electron discharge reaction tends to proceed in a cascade-like manner. As a result, electrons are amplified remarkably.
Furthermore, since the water vapor is introduced into the inner space while the temperature is dropping from the peak, the thermal degradation of the phosphors under the presence of the water vapor will hardly occur. Note here that it is desirable to introduce the water vapor when the temperature is below the point at which the water vapor will react with the phosphors.
Here, the introduction of the water vapor in the water vapor introducing step may be performed when the temperature is in a range of 350xc2x0 C. to 100xc2x0 C.
With this method, the water vapor remains in the inner space of the completed gas discharge light-emitting device efficiently. Also, it becomes easier to improve discharge voltage reduction effects. Furthermore, the thermal degradation of the phosphors, including the blue phosphor which is most susceptible to thermal degradation, under the presence of the water vapor will hardly occur in this temperature range.
Here, the predetermined amount may be adjusted so that a water vapor partial pressure in the inner space once the water vapor has been introduced is no lower than 1.3 kPa (10 Torr) at a normal temperature.
By adjusting the water vapor partial pressure at no lower than 1.3 kPa (10 Torr), the water vapor remains in the device efficiently, with it being possible to enhance the electron amplification action of the water vapor.
Here, a gas medium that includes the water vapor may be introduced into the inner space in the water vapor introducing step.
Here, the sealing in the sealing step may be performed with the phosphors being in contact with a dry gas, at least until the construction elements are heated to the peak temperature.
With this method, the second object can be fulfilled.
Here, the dry gas preferably includes oxygen.